The performance of chemical or biochemical analyses, assays, or preparations often requires a large number of separate manipulations to be performed on the materials or components to be assayed, including measuring, aliquotting, transferring, diluting, mixing, separating, detecting, incubating, etc. Microfluidic technology miniaturizes these manipulations and integrates them so that they can be executed within one or a few microfluidic devices. For example, pioneering microfluidic methods of performing biological assays in microfluidic systems have been developed, such as those described by Parce et al., “High Throughput Screening Assay Systems in Microscale Fluidic Devices,” U.S. Pat. No. 5,942,443 and Knapp et al., “Closed Loop Biochemical Analyzers,” U.S. Pat. No. 6,235,471, the contents of which are incorporated by reference herein.
To perform such diverse and oftentimes complex manipulations, many examples of microfluidic devices comprise complex arrangements of numerous microfluidic elements (e.g., microchannels, wells, microreservoirs, etc.). Additionally, many examples of microfluidic devices incorporate capillary or other similar elements extending from the body structures of the devices. The microelements of microfluidic devices (whether “complex” or “simple” in arrangement or number) are often etched, micro-milled, etc. into substrates. Additionally, as part of the preparation/manufacture of microfluidic devices, the microfluidic elements, capillary elements, and the like, are often filled with a desired fluid, before the specific assays for which the microfluidic device was designed, are performed. Such construction and preparation of microfluidic devices gives rise to several possible concerns. For example, bubbles possibly can be trapped within the microfluidic device (e.g., within a junction or area where a capillary element joins/abuts a substrate layer of the microfluidic device, or within complex or intricate combinations of microfluidic elements, or within microchannels containing large changes in cross-sectional area, etc.). Additionally, mistakes in construction of the microfluidic device (e.g., mistakes in etching or milling) can possibly produce a blocked, misaligned, or mispatterned microelement.
One method currently used to check for such problems involves injecting dyes through the microfluidic device. However, with complex microfluidic element arrangements, it can be difficult to accurately assess each element in the microfluidic device.
A welcome addition to the art would be an easy, non-invasive way to test microfluidic devices containing one or more microfluidic elements and/or capillary elements to verify that the device is functioning properly prior to operation of the device for its intended use (e.g., to confirm that no bubbles exist, or that no microchannels are blocked, etc.). The present invention includes methods and devices that accomplish these objectives.